This invention relates to a speed reducer which can be used in conjunction with the driving unit for the massage member of a massager, a car motor, a car transmission, or a clutch means for an electric motor. The speed reducer of the present invention is particularly useful in place of reduction gears when a large speed reduction ratio is required.
The most common type of speed reducer utilizes gears, especially in situations where a large reduction gear ratio is required and multi-stage gears, worm gears, planetary gears, or harmonic speed changers cannot be utilized. These gears, however, are very noisy and have a restricted reduction gear ratio due to limitations in the gear teeth. The restricted reduction gear ratio makes it difficult or impossible to obtain desired gear ratios and reduces the efficiency of power transfer. Rolling transmission speed reducers, which are driven by friction or traction and have rollers or balls in a planetary gear system, have been widely utilized because they are quieter. An example of such a rolling transmission speed reducer is disclosed in U.S. Pat. No. Re. 26,978.
The acceleration/deceleration mechanism disclosed in U.S. Pat. No. Re. 26,978 does, however, have the following drawbacks:
1. The rollers or balls only contact the inner and outer races at points and this small area of contact causes the allowable contact pressure and the transferred torque to be low. 2. A differential slip is created between the balls or rollers and the inner and outer races which causes large torque and friction losses. FIG. 6 of U.S. Pat. No. Re. 26,978 shows the arrangement of the ball within the races. Among a plurality of balls within the races, some will contact the race at point A, as shown in FIG. 12a of the present invention, while others will contact the race at point B, as shown in FIG. 12b of the present invention. When the point of contact varies in this way, the circumferential speed of the ball at point A is different from that of a ball at point B and slipping consequently results.
3. The low transfer torque limits the deceleration/acceleration ratio even further so that it is only 1 to 10.